Arteries that carry CO2 rich blood from the heart to the gills are called internal bronchial arteries. The ventral aorta arises from the bulbous aorta and extends to the hyoid artery. Four pairs of internal bronchial arteries arise from the ventral aorta.
(i) First afferent branchial artery: The first pair of afferent bronchial arteries arises from the tip of the ventral aorta. They enter the first gill.
(ii) Second afferent bronchial artery: The second pair of afferent bronchial arteries arises from the medial part of the ventral aorta. They enter the second gill.
(iii) Third afferent branchial artery: The third pair of afferent bronchial arteries arises from the medial part of the ventral aorta. They enter the third gill.
(iv) Fourth afferent branchial artery: From the root of the ventral aorta arises the fourth pair of afferent bronchial arteries. They enter the fourth gill.
Branchial arteries arise from each internal bronchial artery. Branch arteries supply blood to each gill lamella.